Fluorescence Study of the Solvation of Fluorescent Probes Prodan and Laurdan in Poly(ε-caprolactone)-block-poly(ethylene oxide) Vesicles in Aqueous Solutions with Tetrahydrofurane
2008 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 24, no 1, 288-295 p.Article in journal (Refereed) Published
Steady-state and time-resolved fluorescence measurements were used to study the relaxation of the microenvironmentof hydrophobic probes 6-propionyl-2-(dimethylamino)naphthalene (prodan) and 6-dodecanoyl-2-(dimethylamino)-naphthalene (laurdan) in systems containing vesicles formed by the amphiphilic diblock copolymer poly(-caprolactone)-block-poly(ethylene oxide) (PCL-PEO) and water/tetrahydrofurane (THF) solvent mixtures. It was found that in caseof prodan, both steady-state and time-resolved emission spectra were composed of two subspectra corresponding tothe emission of prodan molecules located (i) in fairly rigid (effectively viscous) and hydrophobic domains of thevesicles close to the PCL/PEO interface and (ii) in a more polar and less viscous medium (in the bulk solution). Thefraction of the emission from the more polar microenvironment increases with increasing content of THF in the system.Laurdan, in contrast to prodan, appeared to be solubilized preferentially in the hydrophobic domains up to 30 vol %of THF content, and its emission spectra changed only due to swelling of hydrophobic PCL domains by added THF.The study shows that the analysis of the time-resolved emission from a probe distributed in two media is, in principle,possible, but it is quite complex and appreciably less accurate, and the relaxation times are ill-defined averages ofseveral processes. The bimodal or shoulder-containing time-resolved spectra have to be decomposed in pertinenttime-resolved subspectra and treated separately. Another important result of the study is a piece of knowledge concerningthe motion of the probe with respect to the vesicle. In the studied complex system, not only the relaxation of the solventand reorganization of polymer segments around the fluorescent headgroup of the probe affect the emission but alsoa lateral motion of the probe with respect to the nanoparticle within the lifetime of the excited state contributessignificantly to the relaxation and to the relatively slow time-resolved Stokes shift.
Place, publisher, year, edition, pages
American Chemical Society (ACS), 2008. Vol. 24, no 1, 288-295 p.
IdentifiersURN: urn:nbn:se:umu:diva-52465DOI: 10.1021/la702277tISI: 000251916100043OAI: oai:DiVA.org:umu-52465DiVA: diva2:504864